1. Field of the Invention
This invention relates generally to an electrostatic chuck and, more particularly, this invention relates to an electrostatic chuck containing electrodes that are used for chucking a substrate, biasing a substrate and heating a substrate.
2. Description of the Background Art
Electrostatic chucks are known for electrostatically attracting and retaining a substrate such as a semiconductor wafer during wafer processing such as, for example, by physical vapor deposition (PVD), chemical vapor deposition (CVD) and etching. An example of the structure and function of an electrostatic chuck is set forth in U.S. Pat. No. 5,117,121, entitled METHOD OF AND APPARATUS FOR APPLYING A VOLTAGE TO ELECTROSTATIC CHUCK, patented May 26, 1992, Watanabe et al. inventors; this patent is incorporated herein by reference. As taught in this incorporated patent, a pair of electrodes is embedded in a sheet of relatively low resistivity ceramic material, and DC voltage is applied to the electrodes to create an electric field. When a semiconductor wafer is placed on the chuck, the electric field causes charges to accumulate on the backside of the wafer and opposite charges migrate to the surface of the chuck that is supporting the wafer. The oppositely charged surfaces electrostatically attract the semiconductor wafer to the chuck according to the Johnsen-Rahbek effect. Other known electrostatic chucks embed a pair of electrodes in a body of dielectric material to electrostatically attract a semiconductor wafer utilizing a Coulombic effect, i.e., the charges on the backside of the wafer and those on the electrodes attract one another.
In PVD chambers, the electrostatic chuck is typically mounted to a pedestal that is centrally located in the chamber. To RF bias the wafer, RF power is coupled directly to the pedestal, i.e., the pedestal forms a cathode electrode, and the RF power is coupled indirectly through the electrostatic chuck to the semiconductor wafer. As such, RF power losses are experienced due to the indirect coupling of the RF power through the chuck to the semiconductor wafer.
In certain semiconductor wafer processing applications, such as the PVD deposition of titanium on a semiconductor wafer, the semiconductor wafer is advantageously heated to enhance the adhesion of the deposited titanium to the wafer. Typically, a resistive heater is used to supply heat to the wafer. The heater is generally a resistive coil embedded in the ceramic material of the electrostatic chuck, or the heater may be embedded in a plate of stainless steel that is attached to the bottom of the electrostatic chuck. In either case, the heat produced by the heater must couple through the chuck material and the chuck electrode material before reaching the wafer. Such heating from the bottom of the chuck can produce a substantial thermal gradient vertically across the chuck. Furthermore, non-uniform thermal coupling through chuck can produce non-uniform heating of the wafer that results in non-uniform deposition characteristics.
Accordingly, there is a need in the art for an electrostatic chuck with fewer component parts than prior electrostatic chucks and which provides for DC voltage biasing for electrostatic chucking, RF power biasing and semiconductor wafer heating using a single electrode structure.